Method for supplying electricity to a heat-generating pipe utilizing skin effect of a.c.



3,522,440 GENERATING PIPE .C.

MASAO ANDO METHOD FOR SUPPLYING ELECTRICITY TO A HEAT UTILIZING SKIN EFFECT OF A Filed March 28, 1968 INVENTOR.

' MASAO ANDO ATTORNEYS United States Patent O 3,522,440 METHOD FOR SUPPLYING ELECTRICITY TO A HEAT-GENERATING PIPE UTILIZING SKIN EFFECT OF A.C.

Masao Ando, Kanagawaken, Japan, assignor to Chisso Corporation, Osaka, Japan Filed Mar. 28, 1968, Ser. No. 716,726 Int. Cl. H02j 3/00 US. Cl. 307-38 5 Claims ABSTRACT OF THE DISCLOSURE Method for supplying electricity at one time to at least one heat-generating pipe of ferro-magnetic material and at another time to an A.C. load which comprises at one time connecting a plurality of conductor lines connected to a source of A.C. supply, inserted within said heatgenerating pipe in its longitudinal direction in electrically insulated relation from the inner Wall portion of said heat-generating pipe and also electrically connected to the end of said heat-generating pipe remote from the A.C. supply source to provide current flow only through the inner wall portion of said heat-generating pipe and to transmit generated heat from the outer wall of the heatgenerating pipe by the skin effect of the A.C. to the material which is to be heated, and at another time breaking the connection at both ends of said heat-generating pipe while forming the connection from said A.C. supply source, through said plurality of conductor lines to said A.C. load.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to a method for supplying electricity to a heat-generating pipe which utilizes the skin effect of A.C. More particularly, it relates to a method for supplying electricity to a heat-generating pipe of ferromagnetic material which utilizes the skin effect of A.C. and to an A.C. load, such as a liquid transporting pump, by the use of the same insulated conductor lines in such a way that alternating currents are supplied to a heatgenerating pipe through the insulated conductor lines accommodated in said heat-generating pipe and simultaneously to an A.C. load through the insulated conductor lines accommodated in another heat-generating pipe, or at one time alternating currents are supplied to a heat generating pipe through the insulated conductor lines accommodated in said heat-generating pipe and at another time to an A.C. load through said insulated conductor lines.

Prior art There is a disclosure of the present inventor regarding Apparatus for maintaining liquid being transported in a pipe line at an elevated temperature, which utilizes the skin effect of alternating current. (A.C.) in U.S. Pat. 3,293,407.

At first, the principle of said heat-generating pipe will be described with reference to a heat-generating pipe 2 illustrated in FIG. 1 of the drawing. 2 is a pipe of ferromagnetic material and 5 is a conductor, e.g. an insulated electric wire, installed between both the end of the pipe in electrically insulated relation from the pipe 2, one end of which is connected to an A.C. supply source 20 and the other end of which is connected to a terminal 14 of the pipe. When an electric potential of alternating current is supplied from the A.C. supply source 20- to the circuit consisting of the conductor 5 and the pipe 2, the current flowing between the terminals 14 and 15 of the pipe 2 appears only at the skin part of the inner wall portion of the pipe 2 because .of skin effect.

The region through which the current flows is called a penetration depth. If the penetration depth is designated s (cm.), the inner diameter of the pipe is designated d (cm.) and if d s, s can be expressed approximately by a formula:

in which p is the specific resistance of the pipe material used (52 cm.) ,a is the magnetic permeability and f is frequency (cycles/sec). Further if there are three relations between thickness of the pipe t (cm.), penetration depth s (cm.) and length 1 (cm.), t 2S, D S and 12D, the current concentrates in the skin part of the inner wall portion of the pipe 2 and current does not appear in the outer surface zone of the heat-generating pipe in the circuit. Thus Joules heat is generated in the skin part of the inner wall portion of the pipe 2 by the concentrated current and transmitted to the outside of the pipe through the pipe wall and can be utilized in heating various objects.

When a steel pipe is used as the above-mentioned pipe of ferromagnetic material and a commercially available frequency of 510 or 60 c.p.s. is used, the value of S calculated from the above-mentioned formula becomes approximately O.1 cm. Since the thickness of pipe of 0.2 cm. will be sufficient to satisfy the above-mentioned condition, there is no need of selecting a special pipe material or a frequency of A.C. FIG. 2 shows a crosssectional view of such a heat-generating pipe installed together with a liquid transporting pipe line to be heated therewith. 22 is a liquid transporting pipe and there are fixed three heat-generating pipes 1, 2 and 3 over the entire length of the pipe line in substantially axially parallel relation therewith.

However, in case of a pipe line of large capacity such as those used in the transportation of crude oil, heating is necessary only before starting the transportation of liquid. During the time of transportation of liquid, since the temperature in the inside of the pipe line is maintained approximately at a constant temperature by the heat of the liquid being transported, there is no need of heating at all or even when it is needed, it will be suf ficient to heat only to a slight extent. Accordingly, the installation cost of the heat-generating pipe is expensive relative to its short working time, and it is desirous to reduce the installation cost by some means.

It is an object of the present invention to provide a method for supplying electricity to a heating-generating pipe while supplying electricity to other A.C. loads when there is no need of supplying electricity to the heat-generating pipe, without installing any other feeder to said A.C. load.

It is another object of the present invention to provide a method for supplying electricity to a heat-generating pipe with a less expensive installation cost and with a unified management manner.

These objects and other advantages can be attained by the method of the present invention.

SUMMARY OF THE INVENTION According to the method of the present invention, electricity is supplied at one time to at least one heat-generating pipe of ferro-magnetic material through at least one inner conductor line, connected an A.C. supply source inserted within said heat-generating pipe in electrically insulated relation from the inner wall portion of said heat-generating pipe by electrically connecting said inner conductor line to the end of said heat-generating pipe remote from the A.C. supply source and connecting the other end thereof to said A.C. source to provide current BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic circuit diagram of one embodiment of the present invention and FIG. 2 is a cross-sectional view of a heat-generating pipe which utilizes skin effect of A.C. and is installed in contact with a longdistance liquid transportation pipe.

DESCRIPTION OF THE INVENTION According to the method of the present invention, the insulated conductor line supported within the heat-generating pipe in electrically insulated relation can be used for heating of the liquid before starting of liquid transportation and as a feeder line for the power of liquid transporting pumps. The heat-generating pipe 1 in FIG. 1 shows one example of such a method for supplying electricity.

The method of the present invention is further described with reference to the appended drawing.

Although pipes 1, 2 and 3 are entirely the same heatgenerating pipes, the insulated conductor lines accommodated in said pipes are not the same since pipe 1 includes conductors 4, 4 and 4" for a load which requires three phase A.C. The element 11 is a motor for a liquid sending pump, and the liquid is sent from here toward the side of the pipe on which the A.C. supply source is located. Before starting of the liquid pumping, the heatgenerating pipes 1, 2 and 3 are all used for the purpose of heating. In case of pipe 1, by opening a switch 8 and closing switches 18 and 7, A.C. flows through separate lines 4, 4 and 4", and is delivered to the end of the heatgenerating pipe and flows through the skin part of its inner wall portion. When the temperature of the liquid in the pipe line is elevated to a desired value, the heating is stopped, and transportation of liquid is started by supplying electricity only to the pipe 1. Namely, when the switches 18 and 7 are opened and the switch 8 is closed, a three phase A.C. flows through the lines 4, 4 and 4 and motor 11 is energized. If the three currents are balanced and there is no zero phase current, in this case, there will be no eddy current nor heat generation in the pipe as in case of common pipe used as a sheath of the conductor line. The pipes 2 and 3 are not supplied with power when liquid is being transported, but if necessary it is possible to supply electricity in order to use them for heating. Further, by making the arrangement of the conductor lines in these pipes similar to that in the pipe 1, it is possible to make these pipes function similarly to that of the pipe 1. Though FIG. 1 illustrates a case where the load requires three phase A.C., it goes without saying that the same arrangement can be made also in case of single phase A.C. A transformer 21 is used for the change of voltage, when the voltage of the load is not the same as that of the circuit of the heatgenerating pipe, i.e. that of the initial supply source, but it is possible to install a tertiary winding for the use of a relay in order to make the switch automatically controllable. If it is controlled automatically, the shaft between heating and liquid transmission can be carried out safely even when the motor 11 is installed at a location remote from the A.C. supply source because remote control from the location near the A.C. supply source is possible.

As a most suitable example to which the method of the present invention can be applied, a case of crude oil transportation from an oil well in the bottom of the sea can be illustrated. In order to make the equipment in the sea as simple as possible, only oil transmission equipment is provided there, and an A.C. supply source, other auxiliary equipment and controlling means are placed on the land near the beach. There are many crude oils having high viscosity, and even when they have fluidity at the time of drawing up due to the heat of the earth, they may become viscous during transportation. Unless heated in such a case, they cannot be transported.

The present invention exhibits exceedingly superior effectiveness in pipe lines used in the transportation of such oils. Particularly, the lack of need of an additional feeder which connects an A.C. supply source to a load gives better economical advantage with the increase of the length of pipe line.

The method of the present invention looks to be applicable to other heat-generating methods but in reality, only a method involving a heat-generating pipe utilizing the skin effect of AC. can give the effectiveness desired. When other heat-generating method e.g. a case of M1. (mineral insulated) cable which uses a cable insulated with an inorganic substance, is utilized all the heat generated comes from the electric cable and the total potential drop occurs in the electric cable. If a load requires the same quantity of electric current as in case of heating, the potential at the load 11 in FIG. 1 should be zero and not receive electric power from the supply source 20. Accordingly, for example, in order to obtain at the load 11 an electric potential corresponding to of the potential of the supply source 20, it is only possible totransmit a current corresponding to approximately of the current for heating purpose, and as a feeder to the load, the conductor line will be of a capacity exceedingly small. Whereas in the method of the present invention, nearly 90% of the heat generated comes from the body of the heat-generating pipe and only 10% of it is produced in the conductor line. Accordingly, the potential drop in the conductor line is also only 10%. Even when a load requires the same quantity of current as in case of heating, the conductor line has a capacity sufficient to serve also as a feeder. It is desirous to pay attention to increase in heat conduction from a heatgenerating pipe to a liquid transporting pipe by contact or welding when the heat-generating pipe is used to heat the liquid in the transporting pipe.

Further, it is very effective to fill a fluid having a heat conductivity greater than that of air in the clearance part of the heat-generating pipe of the present invention, because an allowable current for an insulated conductor line accommodated in the inside of a heatgenerating pipe is dependent upon an allowable temperature for the insulating material used in the conducfor line, the temperature of the insulating materal is reduced with the increase of the heat conductivity of the material existing in the clearance part of the pipe, and the filling of heat-conductive fluid increases an allowable current for the conductor line. As heat-conductive liquid useful for the above-mentioned purpose, Water, or an aqueous solution of a salt such as sea water is preferred but oils, fats, petroleum oils, alcohols, and aqueous solutions of the foregoing members are also effective. When the insulated conductor line is provided as an insulated cable for high voltage use, the electric field intensity around the surface of the insulated material can be made uniform and hence the durability of the insulating material can be improved by selecting a relatively electrically conductive material from among heat-conductive liquids useful in filling the clearance part of the pipe.

What is claimed is:

1. A method for supplying electricity at one time to at least one heat-generating pipe of ferromagnetic material and at another time to an A.C. load which comprises at said one time connecting a plurality of conductor lines, connected to an A.C. supply source and inserted within said heat-generating pipe in its longitudinal direction in electrically insulated relation from the inner wall of said heat-generating pipe, electrically to the end of said heat-generating pipe remote from the AS. supply source and simultaneously connecting the other end of said heat-generating pipe to said A.C. supply source to provide current flow only through the inner wall portion of said heat-generating pipe and to transmit generated heat in the inner wall portion of said heat-generating pipe through the outer wall portion of said heatgenerating pipe to the material which is to be heated, and at another time breaking the connection at both the ends of said'heat-generating pipe while forming the connection from said A.C. supply source through said plurality of conductor lines to said A.C. load.

2. A method according to claim 1 wherein the clearance 'between the heat-generating pipe and the conductor lines is filled with a heat-conductive material.

3. A method according to claiin 1 wherein said plurality of conductor lines include three conductor lines for three phase A.C.

4. A method according to claim 1 when said plurality of conductor lines include two single phase A.C.

5. A method according to claim 1 wherein the A.C. load is a motor for sending liquid to be heated, and electric lights.

References Cited UNITED STATES PATENTS 3,410,977 11/1968 Ando 2l9--10.49

ROBERT K. SCHAEFER, PrimaryExaminer H. J. HOHAUSER, Assistant Examiner U.S. C1. X.R. 21930O 

